The present invention relates generally to a vehicle seat having an airbag contained therein and in particular to such a seat with a force concentrator adjacent the airbag to concentrate the force of the inflating airbag at a designed seam in the trim cover to ensure deployment of the airbag through the seam.
In recent years, automobile manufacturers have directed increasing attention to providing improved protection for vehicle occupants. One method of doing so is to provide an inflatable airbag mounted to the vehicle seat to proved additional protection to the seat occupant or to an occupant located rearward of the seat.
Generally, seat mounted airbags fall into two different categories. One type deploys from a visible, discrete door on the seat back or seat bottom. Another type of airbag is stowed beneath the seat trim cover and is designed to deploy through the trim cover. An advantage of using an airbag with a discrete door is that deployment of the airbag through a door is used in frontal airbags in steering wheels and instrument panels. The technology for providing consistent and repeatable deployment of the airbag through the door is well developed. A disadvantage is that the airbag is to locations on the seat where the door will not interfere with the comfort of the seat occupant. Another disadvantage is that the seat cover needs a trimmed recess to install the airbag module into, with cost, complexity and appearance issues. If it is desired for the airbag to deploy through the front corner of the seat back, such as the location of a bolster seam, a discrete door cannot be used. Rather, the airbag must be beneath the seat back trim cover, and typically beneath a foam pad, where it does not adversely impact the seat comfort. However, when the airbag deploys through the trim cover, there are considerably more variables involved in providing consistency in airbag deployment and airbag in-position timing.
The seat trim cover provides numerous variables affecting airbag deployment. The trim cover fabric type, such as cloth, leather, vinyl, etc. and combinations of these various types, all behave differently and have different tensile and tear strengths. In addition, different materials of the same types, such as different cloth fabrics have different tensile strengths, tear strengths, and elongation etc. that affect the manner in which an airbag deploys through the trim cover if the trim cover material is ruptured to deploy the airbag. Other variables introduced by the trim cover include the strength of the trim cover scrim layer or backing and the strength of the thin foam layer typically laminated to the trim cover fabric. All of these variables are also effected by high and low temperatures.
Wear of the trim cover over time and trim cover damage by cutting, puncturing, cigarette burns, etc., also introduce variables in airbag deployment. For example, a cut in the trim cover at a location other than the intended deployment can cause the trim cover to rupture at the wrong location, resulting in the airbag being out of position.
Other variations in the deployment can be introduced by the density and type of the seat foam pad, the presence or absence of a border wire embedded in the foam pad, the trim cover attachment locations, the types of attachments and the deployment seam location relative to the airbag module.
To reduce or eliminate the effects of the above trim cover variables, it has been proposed to deploy airbags through a seam in the trim cover by rupturing the seam a opposed to rupturing the trim cover material itself. The seam strength is controlled by the thread strength and not fabric strength. Numerous variables affect the strength of the seam. These include the seam type, number of stitches per inch, thread strength, the seam arrangement, styling and welting. Most of these variables can be controlled in the design of the trim cover. As a result, greater deployment consistency can be achieved with deployment through a trim cover seam. However, even with designed deployment through a seam, the trim cover will introduce variations in airbag deployment. Different elongation characteristics between different trim cover materials will affect deployment. A weak spot may result in the cover tearing instead of the seam.
To eliminate trim cover variability, a force concentrator is used that surrounds the folded airbag and concentrates, or directs, the force of the inflating airbag to the designed deployment seam. This causes the seam to rupture and allow the airbag to deploy therethrough. By directing the force to the seam through the force concentrator, the trim cover material is not loaded. As a result, the trim cover characteristics do not influence the airbag deployment. Consistent bag deployment can be achieved with a variety of different cover materials.
The force concentrator consists of two panels of sheet material joined into the deployment seam and extending away from the seam in opposite directions. The panels extend beneath the trim cover and surround the airbag and a portion of the seat frame. The panel ends distal to the seam are joined to one another, whereby the concentrator panels forming a sleeve circumscribing the airbag and seat frame.
Depending on the location of the airbag and seat frame, one panel of the force concentrator may pass through a slot in the seat cushion pad to meet with, and join to, the distal end of the other panel to form the sleeve. The force concentrator panels are made of a substantially non-stretchable material with a tensile strength sufficient to withstand the force of the inflating airbag without tearing. The concentrator material must be strong enough to transmit the deployment force to the seam and rupture the seam. One material with the necessary tensile strength is the material used to make airbag itself. Other high strength sheet materials may be used as well.
The force concentrator can be mounted to a vehicle seat at any location where it is desired to deploy an airbag. For example, for a side airbag, the force concentrator can be mounted along the side of the seat in the bolster area of either the generally horizontal seat bottom or the generally upright seat back. The force concentrator can also be mounted at the upper end of the seat back of a front seat for rearward inflation to protect a rear seat occupant.
The force concentrator also assists the performance of the airbag by controlling and managing the variable energy output from the airbag due to different climatic conditions. At low temperatures such as -35.degree. C., the gas generator has considerably less energy available compared to its performance at 21.degree. C. An estimate would be a 30 percent drop in gas generator performance at the low temperature. Without the force concentrator directing the available force onto the deployment seam, the trim cover may fail to rupture during the airbag deployment. To overcome this condition, a weaker deployment seam could be used, however, this would have an adverse affect on the durability of the trim cover.
At high temperatures such as 40.degree. C., the gas generator has significantly more energy available. This could lead to failure of the wrong seam and/or damage to the trim cover and its tie downs in the foam pad. The result maybe improper deployment of the airbag. The force concentrator prevents this by containing the force and directing it solely onto the deployment seam. The use of the force concentrator ensures a low temperature deployment by directing the reduced energy available onto the deployment seam. The use of the strongest trim cover deployment seam feasible can then be used for a given low temperature gas generator performance. Furthermore, airbag mal-deployment caused by the wrong seam or trim cover rupture during airbag deployment at high temperatures is prevented by the force concentrator.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.